Acceleration of sulfur-vulcanization of rubber with sulfinic acids and derivatives



United States Patent M 3,518,236 ACCELERATION 0F SULFUR-VULCANIZATION 0F RUBBER WITH SULFINIC ACliDS AND DERIVATIVES Byron A. Hunter, Woodbridge, COHHL, assignor to Uniroyal, Inc., New York, N.Y., a corporation of New Jersey No Drawing. Filed July 20, 1967, Ser. No. 654,705 Int. Cl. C08c 11/54; COSf 27/06; C07d 87/22 U.S. Cl. 26t}79.5 Claims ABSTRACT OF THE DECLOSURE Scorch safety or delayed action acceleration is achieved by using, as accelerators, organic sulfinic acids, metal or amine salts of sulfinic acids, aldehyde reaction products of sulfinic acids (hydroxy sulfones), or aldehyde-amine reaction products of sulfinic acids. Examples are p-toluene sulfinic acid, zinc benzene sulfinate, n-butylamrnonium-p-toluene sulfinate, reaction product of p-toluene sulfinic acid and formaldehyde, reaction product of ptoluene sulfinic acid and ethanolarnine.

This invention is concerned with acceleration of the sulfur-vulcanization of rubber. More particularly, the invention resides in the discovery that organic sulfinic acids, salts of organic sulfinic acids, aldehyde reaction roducts of sulfinic acids, and aldehyde and amine reaction products of sulfinic acids, constitute a highly useful class of rubber vulcanization accelerators.

The application of certain organic sulfur compounds as rubber vulcanization accelerators is well known and widely practiced in the rubber industry. Mercaptobenzothiazole and certain derivatives of mercaptobenzothiazole are highly regarded as vulcanization accelerators and have been employed as such for many years. Derivatives of dithiocarbamic acid have also been used in great quantity but these materials are generally classed as ultra accelerators, being fast in their action and often functioning at relatively low curing temperatures. For many applications in the rubber industry the rapid curing action at low or moderate temperatures is desirable. For other applications, however, the curing action at moderate temperatures is disadvantageous, particularly in cases where the rubber composition is subjected to processing temperatures prior to the curing cycle which activate the accelerator and cause undesirable prccure or scorch. Rubber stock which is scorched during mixing or shaping procedures is difficult to mix or process and often produces cured rubber vulcanizates of inferior quality. For these and other reasons delayed action or safe accelerators have been sought which are relatively inactive at somewhat elevated processing temperatures but become active vulcanization accelerators at higher curing temperatures. The so-called benzothiazole sulfenamides show decided advantages over previously used accelerators as far as scorch safety is concerned and this class of delayed action accelerators now enjoys the wide usage in the rubber industry. However, with continuing trends toward faster and higher temperature processing operations the need for accelerators possessing scorch safety beyond that afforded by the benzothiazole sulfenamides is now clearly recognized.

It is an object of the present invention to provide a new class of rubber vulcanization accelerators which ex- 3,518,236 Patented June 30, 1970 hibit a high degree of scorch safety under relatively high temperature mixing and processing operations but which are effective vulcanization accelerators at higher curing temperatures. It is also an object of the invention to provide rubber vulcanization accelerators which show a higher degree of scorch safety than does N-cyclohexyl benzothiazole sulfenamide and which function as effective vulcanization accelerators at curing temperatures in excess of 300 F. It is a further object to provide rubber vulcanization accelerators which can be readily prepared in high yield at low cost from easily available and low cost intermediates. Another objective is to provide a class of rubber vulcanization accelerators which exhibit a broad spectrum of scorch safety and accelerator activity and from which selected chemical compounds can be chosen for use in specific applications.

I have discovered that organic sulfinic acids and salts of organic sulfinic acids as well as certain derivatives of sulfinic acids are valuable vulcanization accelerators. Thus, I have found that free sulfinic acids and their metal salts exhibit unusual resistance to prevulcanization under normal processing temperatures but function very effectively as vulcanization accelerators at higher curing temperatures. I have also found the scorch and curing properties of organic sulfinic acids can be further modified by producing salts with ammonium or various substituted ammonium radicals as salt forming substituents, or by producing formaldehyde or formaldehyde-amine (or ammonia) derivatives of the sulfinic acids.

The organic sulfinic acids employed in the invention are chemical compounds characterized by the structure:

Treatment of the salt with mineral acid produces the free sulfinic acid (often less stable than the salt) Prepartion of the zinc salt of benzene sulfinic acid is illustrated in the following representation:

SO2C1 NaaSOs ZNaOH SOzNa NazS04 -la l 2 NaSOr Sulfinic acids for use in the invention can also be prepared by reacting aromatic hydrocarbons with sulfur dioxide in the presence of aluminum chloride or by reacting a diazotized aromatic amine with sulfur dioxide in the presence of a copper catalyst.

p-Toluene sulfinic acid can be prepared by reacting p-toluene sulfonyl chloride with sodium sulfite in aqueous caustic, followed by acidification of the resulting solution of sodium p-toluene sulfinate. Treatment of the free acid in an organic solvent (as alcohol) with an amine produces an amine salt of p-toluene sulfinic acid useful in the invention:

To make chemicals useful in the invention, primary, secondary and tertiary amines can be used, among which may be mentioned:

methylamine morpholine ethylamine piperidine n-propylamine dimethylamine iso-propylamine ethanolamine n-butylamine cyanoethylamine secondary butylamine diethylamine tertiary butylamine dipropylamines tertiary octylamine dibutylamine triethylamine laurylamine tributylamine cyclohexylamine amylamine dicyclohexylamine hexylamine benzylamine octylamine trimethylamine dodecylamine ethylenediamine octadecyla-mine dimethylamine propylamine Sulfinic acids also react with formaldehyde and other aldehydes:

where R is H or an organic radical. The latter alphahydroxy sulfone compounds may be utilized as accelerators according to the invention or they may be further reacted with ammonia or primary amines to form compounds which are useful in the practice of my invention:

From the foregoing it will be apparent that the sulfinic acid compounds which are useful as vulcanization accelerators in the practice of my invention cover a wide range of materials, including three general types, as follows:

Type (A): free sulfinic acids and metal salts of sulfinic acids;

Type (B): amine (or ammonium) salts of sulfinic acids; and

Type (C): formaldehyde reaction products of sulfinic acids (i.e., alpha-hydroxy sulfones) and formaldehydeprimary amine (or ammonia) reaction products of sul finic acids.

The foregoing three general types may be represented by four general formulas, as follows:

Types A and B:

4 Type C:

11 n" -s-b-omm III. l

N. If R4 In Formula I, above, R is a monovalent organic radical selected from aryl (e.g., phenyl, biphenyl, naphthyl), alkyl (e.g., methyl, butyl, octyl, etc.), cycloalkyl (e.g., cyclohexyl), in which categories I include equivalent combinations thereof and equivalent substituted forms thereof (e.g., aralkyl [such as benzyl], alkaryl [such as tolyl], halo [e.g., chloro, bromo]-substituted as in chlorophenyl, nitro-substituted as in nitrophenyl, acetamino or acetamido-substituted as in acetamidophenyl, as well as heterocyclic radicals such as 2-benzothiazyl), for example, while n is a number equal to the valence of Y, and Y is selected from (a) hydrogen (b) metal (including univalent and polyvalent metals such as sodium, potassium, lithium, calcium, magnesium, aluminum, barium, zinc, copper, nickel, cadmium, cobalt, tin, lead, iron, etc.)

(c) the radical:

where R R" and R are the same or different and are selected from hydrogen, alkyl (e.g., methyl, propyl, octyl, etc.), cycloalkyl (e.g., cyclohexyl), with or without various substituents such as CN, OI-I, NH etc., and may be combined in a cyclic structure such as piperidyl or morpholyl.

In Formula II, above, R is a divalent organic radical such as alkylene (e.g., methylene, polymethylene, ethylidene, etc.) or arylene (e.g., phenylene, biphenylene, naphthylene), and n and Y are as previously defined.

In Formula III, R is a monovalent organic radical as previously defined for R, or a divalent organic radical as previously defined for R or a higher-valent organic radical; m is a number equal to the valence of R and R is hydrogen, alkyl (e.g., methyl, propyl, octyl, etc.) or aryl (e.g., phenyl, biphenyl, naphthyl).

In Formula IV, R R and m are as previously defined for Formula III, and R and R are the same or different and may have values as defined for R, R and R as set forth above.

The following are examples of sulfinic acid compounds which are useful for the purposes of my invention: p-toluene sulfinic acid, 2,4,5-trichlorobenzene sulfinic acid, zinc benzene sulfinate, calcium benzene sulfinate, barium benzene sulfinate, magnesium benzene sulfinate, lead benzene sulfinate zinc, p-toluene sulfinate, calcium p-toluene sulfinate, barium p-toluene sulfinate, magnesium p-toluene sulfinate, sodium p-toluene sulfinate, t-octylammonium p-toluene sulfinate, n-dodecylarnmonium p-toluene sulfinate, cyclohexylammonium p-toluene sulfinate, dibutylammonium p-toluene sulfinate, triethylammonium p-toluene sulfinate, t-butylammonium p-toluene sulfinate, n-butylammonium p-toluene sulfinate, di methylammonium p-toluene sulfinate, zinc salts of mixed toluene sulfinic acids, zinc 2,5-dimethylbenzene sulfinate, cyclohexylammonium-2,5-dimethyl benzene sulfinate, zinc Z-naphthalene sulfinate, cyclohexylammonium-Z naphthalene sulfinate, dicyclohexylammonium p-toluene sulfinate, methylammonium p-toluene sulfinate, zinc salt of meta benzene disulfinic acid, diethylammonium p-toluene sulfinate, cadmium benzene sulfinate, stannous benzene sulfinate, nickelous benzene sulfinate, cupric p-toluene sulfinate, nickelous p-toluene sulfinate, zinc 2,4,5-trichloro benzene sulfinate, zinc p,p-oxybis (benzene sulfinate), zinc p-chloro benzene sulfinate, zinc butane-1,4-disulfinate,

lners of ethylene and propylene with such dienes as dicyclopentadiene, 1,4-hexadiene, cyclooctadiene, methylene norbornene, ethylidene norbornene, and similar nonconjugated dienes, and the butyl rubber types, that is, rubbery copolymers of isoolefins such as isobutylene zinc p-nltrobenzene sulfinate, p-tolyl hydroxymethyl sulwith dienes such as lsoprene. These may be described 1n fone, p-acetamino benzene sulfinic acid, zinc p-acetamino general as unsaturated, sulfur-vulcanizable diene polymer benzene sulfinate, zinc a-toluene sulfinate, reaction prodrubbers. For purposes of the invention the present acnet of p-toluene sulfinic acid and ethanolamine, reaction celerator is compounded with the dienic unsaturated sulproduct of p-toluene sulfinic acid and ethylene diamine fur-vulcanizable rubber, sulfur, and any desired conven- (2:1), and reaction product of p-toluene sulfinic acid and tional compounding ingredients usually used in sulfur 3-dimethylamino propylamine. vulcanizates, all in conventional proportions. Mixing and The foregoing examples are given as illustrative of the shaping of the vulcanizable composition may be accomsulfinic acid compounds which are useful as accelerators. plished in the conventional manner, and the vulcaniza- It is not intended that the invention be limited to the tion may be accomplished by heating under appropriate specific products listed inasmuch as it will be realized conditions usually used for sulfur vulcanization of rubber, that many other sulfinic acids and sulfinic acid salts may the time and temperature of heataing being in general also be employed. inversely related as in conventional practice. Materials Preferred chemicals are those of Type A as defined of Type A, above, are particularly advantageous for curabove, namely, the free sulfinic acids and their metal ing at What are regarded as highly elevated conventional salts. These exhibit exceptional scorch safety (based on curing temperatures (e.g., 350450 F.). the 270 F. cure data) and are particularly well suited The sulfinic acid compounds may be used as sole acfor relatively high temperatures (circa 350 F.; frecelerators or may be used in combination with other quently 300-400 F. or more) cure. In other words these known accelerators or vulcanization activators known to are high temperature accelerators. In the Type A chemithose skilled in the art. cals which are free acids, R is preferably p-toluene or In order to illustrate the valuable characteristics of 2,4,5-trichlorobenzene. p-Toluene sulfinic acid appears sulfinic acid components as vulcanization accelerators the to be considerably more stable than benzene sulfinic acid following examples (all quantities being expressed as and is therefore a preferred product. In the type A chemiparts by weight) are shown: cals which are metal salts of sulfinlc ac ds, R may have a 0 EXAMPLE I Wide variety of values without restriction, as 1llustrated.

The materials of Type B, above, ammonium or subsynthetlc 0 130 0011 Was prepared, Comstituted ammonium salts, on the other hand, have scorch bllllng the fOlIOWlng g nts In a Banbury mixer, using characteristics approaching conventional accelerators #2 speed and with cooilng Water turned on:

(such as N-cyclohexyl benzothiazole sulfenarnide, for exon extended (375% on) ,butadieng styrene (23% ample), although some of these show a definite advant g styrene) copolymer 1375 as far as scorch rate (at 270 F.) is conc rned. Zinc Oxide (protox 166) Mammals under TY Pe above the or p-Isopropylarnino diphenylamine (Flexzone 3C) 1.5 formaldehydeammomum (or amme) envatwes High abrasion furnace carbon black (Vulcan 3) 68.0 erally fall between Types A and B s far as scorch af y Wax blend (Sunpmof improved) L0 and accelerating characteristics are concerned. In Types stearic acid 10 B and C, the K may have a wide variety of values withpolymerized Petr 01w m hydrocarbon plasticizer out restriction, as described. (paraflux) 30 The sulfinic acid compounds of my invention can be used as accelerators of vulcanization of various elas- 2150 tomeric materials as typified by the conjugated diolefin homopolymers and copolymers of conjugated diolefins above g lg ff zg s as t i i it g fg with copolymerizable monoethylenically unsaturated was en Com me Y ur par S) an e Omers including Such homopolymers as polyisoprene accelerators of the invention 1.2 parts). Comparisons mortl l th h contento Otherwise) 01 were also made with commercial accelators, us1ng 1.75 (Ha i or Syn 1g r d 3 y parts of his benzothiazole disulfide (MBTS) or N-cyclobutadlene (will Slon or so utlon'prepareb F (us-con hexylbenzothiazole sulfenamide (Delac S) 1.25 parts. tent or and copolymers hke utadlene"styre ne Portions of each stock were cured for 45 and 90 minutes copolymer (emulslon or solution-prepared, stereo-specific at R and for 45 minutes at F In addition the othefwlse), butadlene'acfylonltnle copolymer, butastocks were subjected to the Mooney scorch test and dienewmylpyrldme copolymer, the unsaturated, Sulfllfthe so-called scorch time and cure rate were deter vulcanizable olefin copolymer rubbers, such as terpolymined. The data are given in Table I.

TABLE I Cure at 293 F. Cure at 350 F.

Percent Scorch Cul e modulus Tensile elongation 300% P ercent time rate modulus, Tensile, elongation Chemical (270 F.) (270 F.) 45' 45' 00' 45' 45' 45' 45' None (sulfur alone) 00 150 260 1,220 1,180 650 2,320 Bis(l)enzothiazolyl)disulfide (control) 1530 4'30" 1,100 1,280 3,070 2,640 600 560 1,010 2, 620 700 N -cyclohexyl benzothiazole sulfcnamide 660 (control) 1015" 4' 1,150 1,160 3, 000 2,820 600 010 000 2,580 680 Zinc benzene sulfinate 30' 00 430 800 1, 080 2,580 870 050 1,100 2,800 020 Zine p-tolucne sullinate 38 00 440 000 2, 030 2,650 850 660 1,200 2,840 540 Zine-p,p'-oxybis(benzene sulfinate) 60 200 510 700 1,070 1,000+ 760 1,220 3,000 610 Zinc p-chlorobenzone sulflnatenh. 47 60 310 700 1,320 2,320 000 690 1,240 3,130 650 Zincbutane-1,4-disulfinate 60 200 550 700 2,010 1,000 730 370 2, 500 720 Zinc p-nitl'obenzene sulfinate" 56 60 280 700 1,350 2,330 000 700 1,070 2,670 050 p loluene sulfinic acid 41 60 460 830 1,960 2, 590 870 600 1,130 2,870 640 Zinc-alpha-toluene sulfinate 52 60 250 470 1,250 2,300 950 840 870 2,600 760 Reaction product p-toluene sul formaldehyde 34 60 480 930 2, 290 2, 930 820 680 1,140 2, 900 680 Tert.-butyl ammonium p-toluene sulfinatenn 19 36 000 1,240 2,830 2,480 670 500 1,380 3,100 590 TABLE III Cure at 292 F. Cure at 350 F.

300% 300% modulus Tensile Elongation modulus Tensile Elongation Scorch Cure Chemical time rate 45 90 45' 90 45 90 30 45' 30 45' 30 45' Blank (Sulfur alone) 60 150 140 260 1, 220 1, 180 590 650 1,980 2, 320 740 700 BisXbenzothiazyl)disulfide (control) 1330" 3'15 1, 150 1, 270 3, 300 3, 340 620 670 1, 010 1, 040 3, 000 3, 130 630 650 N-cyclohexylbenzothiazole sulienamide (control 15 3'30 1, 190 1, 250 3, 510 3, 260 670 610 970 950 3, 130 3, 110 710 690 Zincfimixed toluene) Sulfinates 29' 60 210 330 780 1, 500 920 930 920 1,010 2, 630 2, 810 640 620 Zinc-2,5-dimethyl benzene sulfinate 48 60 140 200 280 650 l, 070 980 690 800 2, 230 2, 530 660 660 Cyclohexylammonium2,5-dimethyl benzene Sulfinate 27 60 210 350 870 1, 540 830 750 790 840 l, 910 1, 980 540 520 Zinc-2-naphthalene Sulfinato 46 60 130 200 370 700 1, 180 1, 010 600 710 2, 110 2, 320 730 660 Cyclohexylammom'um Z-naphthalenesulfinate..- 60 250 440 1, 100 l, 810 860 750 800 860 2, 420 2, 560 (510 600 Dicyclohexylammonlum p-toluene sulfinate 17'26 30 360 600 1,340 1, 470 710 530 850 960 1, 820 1, 820 510 450 Methylarnmonium-otoluene Sulfinate 60 220 400 150 1, 860 950 810 780 820 2, 520 2, 610 680 660 Reaction product of p-toluene sulfinic acid and ethanolamine 23 44 380 720 1,610 2, 440 820 680 720 820 2,710 2, 550 710 620 Reaction product of p-toluene sultinic acid and ethjylenediamine (2:1) 14' 2215" 590 900 2, 400 2, 900 770 650 1, 130 1, 160 3, 210 3, 050 610 590 D ylamino p-toluene sulfinate 1830 3130 420 900 2, 010 3,000 890 690 1,000 970 2, 870 2, 750 610 610 n-butylemm0nium p-toluene sulfinate. 1830." 3230 350 750 1, 690 2, 720 880 730 880 920 2, 830 2, 690 600 c Reaction product oi p-toluene sulfinic acid and 3- dimethylamino propylamine 1230" 2215" 600 1, 000 2, 660 3, 150 780 640 870 1, 060 2,890 2, 600 620 540 Reaction product of p-toluene sulfinic acid and B-dl 540 900 2, 060 2, 450 750 590 970 1, 070 2, 830 2, 640 620 560 400 870 1, 900 2, 590 860 620 970 1,010 2, 750 2, 880 630 640 Bis'Kp'toluene sulionyl methyl) amine l- 22' 35' 510 760 2, 330 2, 810 880 720 1, 030 1, 060 2,830 2, 690 620 540 TABLE IV Cure at 292 F. Cure at 350 F. Cure at 400 F.

300% 300% 300% modulus Tensile Elongation modulus Tensile Elongation modulus Tensile Elongation Chemical (1.2 parts each) 45 90 45' 90 45 90 30 45 30 45 30 45 15 30 15 30 15 30 N-eyblohexyl benzothiazole sulfenamide (control) 1,150 1, 220 3, 200 3, 360 630 610 970 1,020 3, 190 3,100 560 640 750 810 2, 690 2, 590 710 670 Cadmium benzene sulfinate. 250 420 450 1, 660 960 970 840 950 2, 660 2, 690 650 620 900 930 2, 610 2, 520 660 610 Stannous benzene sulfinate l. 300 220 960 1, 050 910 800 860 1,840 2, 260 530 560 760 910 1,900 2,100 560 560 N iclr'elous benzene sulfinate... 200 380 260 1, 190 1, 070 890 920 980 2, 630 2, 910 640 650 920 1,080 2, 540 2, 410 630 550 Cupi'io p-toluene sulfinate 200 250 240 670 900 740 710 740 2, 060 2, 090 640 500 790 850 2, 250 2,250 640 600 Nickelous p-toluene sulfinate 210 560 420 1, 950 1, 010 820 980 1, 100 2, 850 2, 700 620 560 l, 010 1, 120 2, 650 2, 340 600 550 Having thus described my invention, what I claim and desire to protect by Letters Patent is:

"1. In a method of accelerating the sulfur vulcanization of a sulfur-vulcanizable unsaturated rubber, the improvement comprising using as the accelerator a chemical selected from the group consisting of those of the formulas:

wherein R is a monovalent organic radical selected from aryl, alkyl, cycloalkyl, and Z-benzothiazyl radicals, n is a number equal to the valence of Y, Y is selected from (a) hydrogen (b) metal and (c) the radical:

where R R and R are the same or different and are selected from hydrogen, alkyl, cycloalkyl, piperidyl and morpholyl, R is a divalent organic radical selected from alkylene and arylene, R is selected from (i) R as previously defined and (ii) R as previously defined wherein R is a monovalent organic radical selected from aryl, alkyl, cycloalkyl, and Z-benzothiazyl radicals, n is a number equal to the valence of Y, Y is selected from (a) hydrogen (b) metal and (c) the radical:

Where R R and R are the same or diflerent and are selected from hydrogen, alkyl, cycloalkyl, piperidyl and morpholyl, R is a divalent organic radical selected from alkylene and arylene, R is selected from (i) R as previously defined and (ii) R as previously defined 1 1 m is a number equal to the valence of R R is selected from hydrogen, alkyl, and aryl, and R and R are the same or difierent and have values as defined above for R, R' and R 3. A method as in claim 1 in which the accelerator of the said formula is a sulfinic acid.

4. A method as in claim 1 in which the accelerator of the said formula is a metal salt of a sulfinic acid.

5. A method as in claim 1 in which the accelerator of the said formula is an amine or ammonium salt of a sulfinic acid.

6. A method as in claim 1 in which the accelerator of the said formula is an alpha-hydroxy sulfone.

7. A method as in claim 1 in which the accelerator has the Formula IV.

8. A method as in claim 1 in which the rubber is selected from the group consisting of polybutadiene, polyisoprene, and butadiene-styrene copolymer.

9. A method as in claim 1 in which the rubber is butadiene-styrene copolymer.

10. A method as in claim 1 in which the accelerator is zinc benzene sulfinate.

11. A method as in claim 1 in which the accelerator is zinc p-tolueune sulfinate.

12. A method as in claim 1 in which the accelerator is tert. butyl ammonium p-toluene sulfinate.

References Cited UNITED STATES PATENTS 2,750,357 6/1965 Bredereck et a1. 260--77.5

FOREIGN PATENTS 900,172 7/1962 Great Britain.

JOSEPH L. SCHOFER, Primary Examiner C. A. HENDERSON, 1a., Assistant Examiner U.S. Cl. X.R.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 518, 236 Dated June 3 1970 Inventofle) Myron A. Hunter It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 10, lines 50-52, formula III should read:

O H 2 H R -S-COH I! o R Co1 11, line 24, "tolueune should read --to1uene.

SIGNED FINE QFAIED lam/10m (SEAL) Attest:

EdwardM. Kashmir mm B. W, .38.

Attesnng Offiwl oomrissioner o1 PatentqJ 

